Belt force sensor

ABSTRACT

An occupant restraint assembly and for a motor vehicle operates to sense the tension forces on a seat belt to detect the presence of a human occupant or a child restraint seat. A sensor attached to the seat belt measures tension forces. The sensor is mounted in line with the seat belt. A strain gauge senses tension on the seat belt. An additional embodiment of the sensor includes three prongs attached to a common beam that allow the sensor to be slipped onto the seat belt without modification to the seat belt. A middle prong includes the strain gauge to sense movement relative to outside prongs. The seat belt threads over the outside prongs and under the middle prong such that tension on the seat belt forces the middle prong transversely to tension exerted on the seat belt.

[0001] This application claims priority to provisional applicationsserial No. 60/177,888 and No. 60/177,887 filed on Jan. 24, 2000.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a passenger restraint assembly having asensor for detecting seat belt tension to indicate the presence of achild restraint seat.

[0003] Typically, a motor vehicle will include an air bag system todeploy an air bag cushion to protect passengers in the event of acollision. Air bag cushion deployment must necessarily by quick in orderto prevent injury caused by the collision. The speed of deployment ofthe air bag cushion and the accompanying force of the inflating air bagcushion makes deployment of the air bag cushion to protect smallchildren undesirable. Further, the use of a child restraint seat is notcompatible with the intended operation of the air bag system. Althoughwarnings of and prohibitions against the seating of children or the useof child restraint seats where an air bag may deploy are now standard invehicles equipped with an air bag system, such warning may be ignored,causing undesirable results.

[0004] Passive warnings and notices may be supplemented with an activesystem that senses the type of occupant utilizing the seat and disablesair bag deployment based on predetermined criteria. One such systemknown in the art is a weight based occupant detection system. Aweight-based system includes sensors placed in the seat that allow adetermination of the weight of the occupant in that seat. Such systemsare set to disable the air bag upon a determination that an occupant isbelow a certain predetermined weight. Such systems work well, however,such a system can be fooled by the placement of child restraint seatover the weight sensors. Typically, the child restraint seat is securedto a seat of a motor vehicle by threading the seat belt around orthrough the child restraint seat. The seat belt of the motor vehicledoes not actually secure the child as is normal when used to secure andadult. Instead the seat belt is used to secure the seat, and then theseat secures the child. Because the seat belt is securing the childrestraint seat, it will be pulled tighter than when normally used tosecure a human occupant. Pulling of the seat belt tightly around thechild restraint seat will provide a large force on the seat, and therebythe weight sensors. Such a force can fool the weight sensor system intobelieving that a large adult is seated in the passenger seat rather thanthe child restraint seat and therefore not disable deployment of the airbag cushion.

[0005] For these reasons it is desirable and necessary to develop amethod and device that can detect and differentiate between the presenceof an adult occupant and a child restraint seat such that deployment ofthe air bag cushion can be disabled when the seat is occupied by a childrestraint seat.

SUMMARY OF THE INVENTION

[0006] The invention is an assembly and method for sensing the tensionforces on a seat belt such that a determination can be made as to thepresence of a human occupant or a child restraint seat.

[0007] The assembly includes a seat belt attached to an interior supportof the motor vehicle. Attached to the seat belt is a sensor thatmeasures the tension forces exerted on the seat belt. Forces above apredetermined magnitude not tolerable by the human occupant indicatesthe presence of a child restraint seat and thereby provides theinformation needed to signal disable deployment of the air bag cushion.The sensor of a first embodiment is mounted in line with the seat beltby looping ends of the seat belt through the sensor. A center section ofthe sensor connects a strain gauge to detect tensile forces exerted onthe seat belt. The strain gauge is electrically connected to acontroller mounted within the motor vehicle for use in determining ifdeactivation of the air bag is necessary.

[0008] Another embodiment of the invention includes three prongsattached to a common beam. A middle prong includes the strain gauge thatoperates to sense movement relative to at least two outside prongs. Theseat belt is threaded over the outside prongs and under the middleprong. This configuration provides for the installation of the sensorwithout modification to the seat belt. Tension on the seat belt operatesto force the middle prong to move substantially perpendicular to thetension of the belt. The strain gauge mounted on the middle prong sensesthe amount of movement and signals the controller. The amount ofmovement of the middle prong is proportional to the tension force placedon the belt, which is used to determine the presence of an adultoccupant or a child restraint seat.

[0009] The invention also includes a method of differentiating betweenthe presence of a human occupant and a child restraint seat in a motorvehicle. The method includes the steps of sensing tension exerted on aseat belt, communicating the magnitude of the sensed tension to acontroller, comparing the magnitude of tension to a predeterminedtension, and determining that a child restraint seat is present if thesensed tension is greater than the predetermined tension.

[0010] The method and assembly of the subject invention provides thenecessary information to detect and differentiate between the presenceof an adult occupant and a child restraint seat such that deployment ofa vehicle air bag can be prevented when a child restraint seat occupiesthe seat

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

[0012]FIG. 1 is perspective view of a seat and the occupant restraintassembly positioned within a motor vehicle;

[0013]FIG. 2 is a perspective view of the first embodiment of the forcesensor;

[0014]FIG. 3 is an exploded view of the first embodiment of the forcesensor;

[0015]FIG. 4 is a view of the first embodiment enclosed in the housing;and

[0016]FIG. 5 is a perspective view of a second embodiment of the forcesensor with the seat belt attached.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Referring to the Figures, wherein like numerals indicate like orcorresponding parts throughout the several views, the subject inventionis an occupant restraint assembly generally shown at 10 in FIG. 1. Theassembly 10 includes a seat belt 12 having two sections 14, 16 and asensor 18. The assembly 10 is disposed within the interior of a motorvehicle 20 having an air bag system 22. A controller 24 is disposedwithin the motor vehicle 20 and communicates with the sensor 18 byelectrical leads 26. The controller 24 also is in communication with theair bag system 22. Typically the air bag system 22 is disposed within adashboard 28 and positioned to provide protection to a passenger seatedin a passenger seat 30. It will be appreciated to those knowledgeable inthe art that the subject invention may be placed anywhere and integratedinto any seat belt restraint system positioned anywhere within the motorvehicle 20 and coupled with the air bag system 22. The sensor 18, ispreferably located on the static or non retracting section of the seatbelt 12.

[0018] Referring to FIG. 2, the sensor 16 includes prongs 32 that extendfrom a common beam 34. The prongs 32 include a middle prong 36 disposedbetween two outside prongs 38. A strain gauge 40 is disposed on themiddle prong 36 for sensing movement of the middle prong 36. The straingauge 40 may be of any type known by a worker knowledgeable in the art.The strain gauge 40 is electrically attached to the controller 24 of themotor vehicle 20 by way of the leads 26.

[0019] The sensor 18 is attached by threading the seat belt 12 over theoutside prongs and under the middle prong 36 creating a loop 42 in theseat belt 12. Tension on the seat belt 12, in the direction indicated byarrows A, force the loop 42 to straighten, thereby exerting a force onthe middle prong 36 in a direction transverse to the tension on the seatbelt as indicated by arrow B. The movement of the middle prong 36 causedby the straightening of the seat belt 12 is sensed by the strain gauge40. Movement of the middle prong 36 is proportional to the tensionexerted on the seat belt 12 and therefore provides for a measurement ofthe forces exerted on the seat belt 12 and that measurement iscommunicated to the controller 24.

[0020] Referring to FIGS. 3 and 4, a housing 44 and cover 46 enclosesthe sensor 18 to protect against errant contact. The housing 44 andcover 46 also conceals the sensor 18 and accompanying leads 26 toprovide a more pleasing appearance. The housing 44 and cover 46 arepreferably fabricated from plastic and are assembled by a simple snapfit configuration 48. As appreciated, the housing 44 and cover 46arrangement may be of any type known in the art.

[0021] An additional embodiment discloses an incline sensor 60 and isshown in FIG. 5. The incline sensor 60 of the additional embodimentincludes a tensile section 50 disposed between belt ring sections 52.The incline sensor 60 is attached in line with the seat belt 12 bysplicing the sensor 60 into the seat belt 12. Splicing is accomplishedby looping ends 54 of the seat belt 12 through the belt ring sections 52and securing the seat belt 12 back onto itself. A strain gauge 56 isdisposed on the tensile section 50 and is electrically connected to thecontroller by leads 26. The strain gauge 26 measures tension on the seatbelt 12, (shown by arrows C). Measurement of tension exerted on the seatbelt 12 is directly measured because the incline sensor 60, being inline with the seat belt 12 encounters the tension in the same directionand magnitude as the seat belt 12.

[0022] The measured tension is communicated to the controller 24 andcompared to a predetermined tension. The predetermined tension is of amagnitude greater than that normally exerted on a human occupant thatwould not be tolerable to the human occupant, but would by indicative ofthe magnitude of force exerted on the seat belt 12 to hold a childrestraint seat 58 (shown in FIG. 1) in place.

[0023] The subject invention also includes a method of differentiatingbetween a human occupant and the child restraint seat 58 such that theair bag system 22 can be disabled if the child restraint seat 58 isdetected. The method includes the sensing of the tension exerted on theseat belt 12 by providing a sensor 18, 60, on the seat belt 12 tocommunicate the magnitude of tension on the seat belt 12 to thecontroller 24. As described above, tension is sensed by the use ofstrain gauge 40, 56 disposed on the sensor 18,60. The strain gauge 40,56senses the amount of strain placed on the sensor 18,40 by the seat belt12. The sensed tension is compared to the predetermined tension. Asdescribed above, the predetermined tension is a tension determined to beintolerable to a human occupant and indicative of the magnitude oftension commonly used to secure the child restraint seat 58 within themotor vehicle 20. If the magnitude of tension on the seat belt 12 isbelow the predetermined magnitude, the air bag system 22 will remainenabled. However, if the measured magnitude of tension is above thepredetermined magnitude, the air bag system 22 will be disabled due tothe indication of the presence of the child restraint seat 58.

[0024] The foregoing description is exemplary and not just a materialspecification. The invention has been described in an illustrativemanner, and should be understood that the terminology used is intendedto be in the nature of words of description rather than of limitation.Many modifications and variations of the present invention are possiblein light of the above teachings. The preferred embodiments of thisinvention have been disclosed, however, one of ordinary skill in the artwould recognize that certain modifications are within the scope of thisinvention. It is understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

What is claimed is:
 1. An occupant restraint assembly for a motorvehicle having an air bag system, said assembly comprising; a seat beltassembly having at least two sections lockable to each other; a sensorassembly attached to at least one of said belt sections that operates tosense tension on said belt; a controller electrically connected to saidsensor and the air bag system such that a magnitude of tension on saidbelt above a predetermined magnitude indicates the presence of a childrestraint seat.
 2. The assembly of claim 1, wherein the motor vehicleincludes an air bag system, and said controller communicates with saidair bag system and disables deployment of said air bag system upon theindication of the presence of the child restraint seat.
 3. The assemblyof claim 1, wherein said sensor assembly includes a strain gauge thatoperates to sense strain on said sensor and thereby tension on saidbelt.
 4. The assembly of claim 1, wherein said sensor is attached inline with one of said belt sections.
 5. The assembly of claim 3 whereinsaid sensor includes a carrier having a tensile section and said straingauge is disposed within said tensile section.
 6. The assembly of claim5, wherein said carrier includes two belt loops disposed on oppositeends of said tensile section, and said sensor is attached in line withone on of said belt sections at said belt loops.
 7. The assembly ofclaim 1, wherein said sensor includes three prongs extending from acommon beam that can be attached to said belt sections withoutmodification of said belt.
 8. The assembly of claim 7, wherein a middleprong is disposed between outside prongs and includes a strain gaugethat operates to measure movement of said middle prong.
 9. The assemblyof claim 7, wherein, said belt is threaded through said prongs such thattension on said belt operates to force said middle prong in a directiontransverse to the tension on said belt and tension on said belt isproportional to the movement of said middle prong such that tensionforces on said belt can be determined.
 10. The assembly of claim 1,wherein said sensor includes three prongs extending from a common beamand said belt is threaded over said outside prongs and under said middleprong such that tension on said belt will force movement of said middleprong in a direction transverse to said tension forces on said belt. 11.The assembly of claim 1, wherein said sensor is disposed in a housinghaving a cover.
 12. The assembly of claim 11, wherein said housing isfabricated from plastic and said cover snaps onto said housing.
 13. Anoccupant restraint assembly for a motor vehicle having an air bagsystem, said assembly comprising; a belt assembly having at least twosections for locking engagement; a sensor assembly having a tensilesection and belt loop sections disposed on opposite sides of saidtensile section, said sensor attached to said belt loop sections suchthat said sensor is in line with said belt; a strain gauge disposed onsaid tensile section that operates to sense strain on said sensor andthereby tension on said belt. a controller electrically connected tosaid sensor and the air bag system such that a magnitude of tension onsaid belt above a predetermined magnitude operates to disable deploymentof the air bag system.
 14. A seat belt tension sensor assembly for amotor vehicle having a seat belt assembly and an air bag system, saidassembly comprising; at least three prongs extending from a common beam,said prongs attached to said seat belt without modification of the seatbelt; a strain gauge disposed on one of said prongs to generate a forcesignal representative of a force exerted on the seat belt.
 15. Theassembly of claim 14, wherein said force signal is received by acontroller disposed within the motor vehicle, said controller signalsthe air bag system to disable deployment of the air bag system if theforce signal exceeds a predetermined magnitude that indicates thepresence of a child restraint seat.
 16. The assembly of claim 14,wherein said prongs are further defined as a middle prong disposedbetween outside prongs and said strain gauge is disposed on said middleprong to measure movement of said middle prong.
 17. The assembly ofclaim 14, wherein the seat belt is threaded through said prongs suchthat tension on the seat belt operates to move said middle prong in adirection transverse to tension on the seat belt, movement of saidmiddle prong being proportional to tension on the belt such that tensionforces on the seat belt are measured.
 18. The assembly of claim 14,wherein said prongs are further defined as a middle prong and outsideprongs and the seat belt is threaded over said outside prongs and undersaid middle prong such that tension on the seat belt forces movement ofsaid middle prong in a direction transverse to said tension forces onthe seat belt.
 19. The assembly of claim 14, wherein said sensor isdisposed in a housing having a cover.
 20. The assembly of claim 14,wherein said housing is fabricated from plastic and said cover snapsonto said housing.
 21. A method of differentiating between the presenceof a human occupant and a child restraint seat in a motor vehicle, saidmethod comprising the steps of; sensing tension exerted on a seat belt;communicating the magnitude of the sensed tension to a controller;comparing the magnitude of tension to a predetermined tension; anddetermining that a child restraint seat is present if the sensed tensionis greater than the predetermined tension.
 22. The method of claim 21,wherein the motor vehicle includes an air bag system, and furtherincludes the step of disabling deployment of the air bag system upondetermining the presence of the child restraint seat.
 23. The method ofclaim 22, wherein the predetermined tension is further defined as thetension that is normally not tolerable for human occupants and thatwhich is normally exerted to secure a child restraint seat in place. 24.The method of claim 23, wherein the sensing step further includes thestep of providing a sensor disposed on the seat belt having a straingauge to sense tension forces exerted on the seat belt.